Serious Bacterial Infections in Young Infants With Viral Infections

Source: Chessex VJ, Barbey FA, Haberstich P, et al. Limitations of comprehensive respiratory viral testing in managing young infants with fever. J Pediatr. 2025;289:114882; doi: 10.1016/j.jpeds.2025.114882.Investigators from KSA Children’s Hospital Aarau, Aarau, Switzerland, conducted a retrospective study to evaluate the association between results of comprehensive respiratory virus testing and risk of serious bacterial infection (SBI) in febrile young infants. Study participants were full term infants ≤90 days old or preterm infants ≤52 postmenstrual weeks of age with a documented rectal temperature ≥38.0°C who were evaluated at a single institution between 2017 and 2022. Only patients for whom comprehensive respiratory viral testing was obtained were included in the analyses. For the viral testing, nasopharyngeal samples were obtained, and PCR was used to test for adenovirus, coronavirus, influenza A/B, metapneumovirus, para-influenza viruses, respiratory syncytial virus (RSV), rhino/enterovirus, and SARS-CoV-2. SBI included urinary tract infection (UTI), bacteremia, and meningitis. The medical records of study participants were reviewed. In addition to demographic data, information on bacterial cultures, viral testing results, initial clinical appearance (ill-appearing or not), and apparent source of fever were abstracted. The primary outcome was diagnosis of SBI, and secondary analysis was specific SBI. The rate of SBI among patients with a positive respiratory virus test was compared to that among all participants, and the risk ratio (RR) was calculated. Subgroup analyses among infants with specific demographic or clinical characteristics also were conducted.Data were analyzed on 456 febrile young infants in whom comprehensive respiratory virus testing was performed. The mean age of study patients was 41 days, and 77.6% had a positive virus test. There were 70 (15.4%) infants with SBI, including 63 with UTI, 6 with bacteremia, and 1 with bacterial meningitis. There was no significant difference in the rate of SBI among participants with positive virus testing results compared to all participants (11.9% vs 15.4%; RR, 0.77; 95% CI, 0.50, 1.05). There also was no significant difference in rate of bacteremia among patients with positive virus tests and all participants (1.3% vs 0.6%; RR, 0.43; 95% CI, 0, 1.11). Among the group of full-term infants who did not appear ill, there were no significant associations between viral respiratory test results and risk of SBI in those with an apparent source of fever, those ≥29 days old, or those <29 days of age. Patients who tested positive for influenza A/B or RSV were significantly less likely to have an SBI (RR, 0.4; 95% CI, 0, 0.9; and RR, 0.2; 95% CI, 0, 0.5, respectively) compared to all participants.The authors conclude that comprehensive respiratory virus test results were not associated with the risk of SBI in febrile young infants.Dr Bechtel has disclosed no financial relationship relevant to this commentary. This commentary does not contain a discussion of an unapproved/investigative use of a commercial product/device.Concomitant SBIs in febrile young infants (FYI) with positive viral testing has been a subject of previous research.1,2 For infants with RSV, influenza, or SARS-CoV-2 infection, rates of SBI may be considerably lower.3,4 (See AAP Grand Rounds. 2025;54[4]:42.)5 In the current study, among 456 FYI who were hospitalized, 15.4% had SBI. Infants with a positive viral test result had an SBI rate of 11.9%, with lower rates observed in those testing positive for influenza and RSV. However, comprehensive respiratory viral testing showed limited value for SBI risk stratification in FYI. It did not significantly support clinical decision-making or replace established risk stratification methods, such as inflammatory markers and urinalysis, for excluding concomitant SBI. Regardless of viral test results, 93% of SBI cases had abnormal inflammatory markers or urinalysis. Additionally, SBI occurred in both virus-positive and virus-negative infants. Thus, for its cost, comprehensive viral testing is not helpful in discriminating which FYI has SBI compared with inflammatory markers.The current study has several limitations. The first is its retrospective design, which left investigators unblinded to the final SBI status and introduced bias during data collection and analysis. The second is that the researchers focused only on hospitalized FYI, limiting generalizability to settings where older infants often are managed as outpatients. Finally, the overall sample size, particularly the number of infants with invasive bacterial infection and for specific viral subgroups (eg, adenovirus, coronaviruses, metapneumovirus), was limited, reducing statistical power for subgroup analyses.Comprehensive viral testing is not associated with improved risk stratification and is more expensive than inflammatory markers and urinalysis for excluding SBI in FYI. Targeted testing may be a more resource-efficient strategy for this population.